In the first clinical study, 39 healthy subjects (53 +/- 11 years old; 20 males and 19 females) had a total daily NaCl intake of 50 mmol (low-salt) and 150 mmol (high-salt) for 4 weeks each, in random order. Ambulatory blood pressure (ABP) and marinobufagenin (MBG) in plasma and urine were measured at baseline (unstandardized salt intake) and after high- and low-salt intake. At baseline, plasma MBG (P-MBG) was related to 24-hour systolic (r= 0.43, P=0.007) and diastolic (r=0.32, P=0.047) BP. Interestingly, gender-specific analyses revealed that these relationships were significant in males only. Compared to low-salt, high-salt diet increased P-MBG (P=0.029), mainly driven by results in men. Male P-MBG responders vs. non-responders (above vs. below median of high-salt induced P-MBG increase) had markedly enhanced systolic (10.4 +/- 6.4 vs. 0.0 +/- 6.0 mmHg; P=0.003) and diastolic (6.7 +/- 5.0 vs. -0.6 +/- 3.6 mm Hg; P=0.001) BP salt sensitivity. We conclude that in males MBG increases with 24-hour ABP, and similar to Dahl-S, 4-weeks of high-salt induced MBG response is accompanied by marked increase in salt sensitivity. However, these patterns seem to be gender specific and are not observed in human females. In the second experiment we studied three groups of male Dahl-S (n=6 each): rats on a low salt (0.1% NaCl) diet (LS); rats on a high salt (8% NaCl) diet for 7 weeks (HS); and rats on a high salt diet for 7 weeks, followed by 3E9 anti-MBG mAb treatment for 1 week (HSAB). SBP, ECHO parameters, creatinine clearance, levels of MBG, weights of aortae, left ventricles (LV) and kidneys were assessed. In HS vs. LS, SBP increased by 74 mm Hg (P<0.01), plasma MBG doubled (P<0.05), renal MBG excretion increased 6-fold (P<0.01), tissue weights increased (LV: 2.37 +/- 0.05 vs. 1.62 +/- 0.04 g/kg BW, P<0.01; aorta: 4.44 +/- 0.17 vs. 3.01 +/- 0.06 mg/mm per kg BW, P<0.01; kidneys: 11.29 +/- 0.2 vs. 8.37 +/- 0.11 g/kg BW, P<0.01), LV fractional shortening decreased (46 +/- 1.2% vs. 58 +/- 2%, P<0.01), and creatinine clearance decreased (1.94 +/- 0.25 vs. 2.61 +/- 0.18 mg/mL, P<0.01). A single intra-peritoneal administration of anti-MBG monoclonal antibody to hypertensive DS (HSAB group) reduced SBP by 35 mm Hg (P<0.01) after just 1 week, markedly reduced weights of LV (2.03 +/- 0.08 g/kg BW, P<0.01), aortae (3.72 +/- 0.06 mg/mm per kg BW, P<0.05), and kidneys (10.7 +/- 0.29 g/kg BW, P<0.05), increased LV fractional shortening (52 +/- 1%, P<0.05) vs. HS group, and restored the creatinine clearance to control (LS) levels (2.82 +/- 0.22 mg/mL, P<0.05). In hypertensive DS there was a tissue-specific pattern of up-regulation of expression of genes, implicated in TGF-beta-signaling (LV: TGF-beta1, TGF-beta2, MAPK3, CTGF, SMADs, collagen-1; aorta: TGF-beta1, TGF-beta2, TGF-beta3, PDGF, fibronectin, SNAIL1, collagens; kidneys TGF-beta1, ITGB1, collagen-1), that was down-regulated following immunoneutralization of MBG. Thus, immunoneutralization of heightened MBG levels in Dahl-S normalized renal function and produced an anti-hypertensive and an anti-remodeling effect associated with down-regulation of genes implicated in TGF-beta-induced fibrosis initiated by MBG in salt-sensitive hypertension.